Electric Power Research Institute Research Articles

Measurement of Aerosol Transmission Through a Stress Corrosion Crack–Like Geometry

The formation of a stress corrosion crack (SCC) in the canister wall of a dry cask storage system (DCSS) has been identified as a potential issue for the long-term storage of spent nuclear fuel. The presence of a SCC in a storage system could represent a through-wall flow path from the canister interior to the environment. Modern, vertical DCSSs are of particular interest due to the commercial practice of using relatively high helium backfill pressures (up to approximately 800 kPa) in the canister to enhance internal natural convection. This pressure differential offers a comparatively high driving potential for blowdown of any particulates that might be present in the canister in the event of a through-wall SCC. In this study, the rates of gas flow and aerosol transmission of a spent fuel surrogate through an engineered microchannel with dimensions representative of a SCC were evaluated experimentally using coupled mass flow and aerosol analyzers. The microchannel was formed by mating two gauge blocks with a linearly tapering slot orifice nominally 13 μm (0.0005 in.) tall on the upstream side and 25 μm (0.001 in.) tall on the downstream side. The orifice is 12.7 mm (0.500 in.) wide by 8.89 mm (0.350 in.) long (flow length). Surrogate aerosols of cerium oxide (CeO2) were seeded and mixed with either helium or air inside a pressurized tank. The aerosol characteristics were measured immediately upstream and downstream of the simulated SCC at elevated and ambient pressures, respectively. The next iteration of testing involves replacing the engineered microchannel with lab-grown SCCs. Preliminary clean flow testing has been conducted on SCC samples provided by the Electric Power Research Institute. These data sets demonstrate a new capability to characterize SCCs under well-controlled boundary conditions. Preliminary testing efforts are focused on understanding the evolution in both the size and quantity of a hypothetical release of aerosolized spent fuel particles from failed fuel cladding into the canister interior, and ultimately, through a SCC.

I-LAMP: Global, Industrywide Learning Aging Management Program for Neutron-Absorber Materials in Spent Fuel Pools

Neutron-absorber materials are used in spent fuel pool (SFP) storage racks to increase storage capacity while maintaining criticality safety margins. Previously, the Electric Power Research Institute (EPRI) proposed a global, industrywide learning aging management program (i-LAMP) as an alternative monitoring program as part of an aging management program. This proposal, along with other EPRI work, was accepted as a concept to close the issued generic letter by the regulator. Since then, EPRI has been working with EPRI-member utilities around the world on data collection. Furthermore, recently, a utility removed two neutron-absorber panels from an operating SFP to meet a regulatory commitment made prior to the i-LAMP proposal. Because of their age and unique history, these panels provided a unique opportunity not only to analyze the conditions of the panels, but also to potentially bound i-LAMP. This paper presents i-LAMP development to date with a focus on BORAL analysis results for these two unique panels, pilot pools as case studies to demonstrate the i-LAMP implementation, and a proposal for a path forward.

Synthesis Load Model With Renewable Energy Sources for Transient Stability Studies

Increased penetration of renewable energy sources (RES) has brought challenges to load modelling techniques. This paper proposes a synthesis load model with RES (SLMR), and elaborates related industrial practice conducted by China Electric Power Research Institute. Several practical issues are addressed in designing and implementing SLMR, such as load survey and representation of different types of RESs. Besides, three new modelling concerns brought by RESs are novelly addressed in the paper, i.e., aggregation of various RES parameters, consideration of various RES terminal voltage, and additional line loss due to RES response. Parameterization of the SLMR calibrates widely varied node voltage in distribution grid, and aggregates them to one equivalent node. The proposed SLMR is practically applied in industrial works, which is demonstrated in the paper.

Intelligent Power System Stability Assessment and Dominant Instability Mode Identification Using Integrated Active Deep Learning.

Simulation analysis is critical for identifying possible hazards and ensuring secure operation of power systems. In practice, large-disturbance rotor angle stability and voltage stability are two frequently intertwined stability problems. Accurately identifying the dominant instability mode (DIM) between them is important for directing power system emergency control action formulation. However, DIM identification has always relied on human expertise. This article proposes an intelligent DIM identification framework that can discriminate among stable status, rotor angle instability, and voltage instability based on active deep learning (ADL). To reduce human expert efforts required to label the DIM dataset when building DL models, a two-stage batch-mode integrated ADL query strategy (preselection and clustering) is designed for the framework. It samples only the most helpful samples to label in each iteration and considers both information contents and diversity in them to improve query efficiency, significantly reducing the required number of labeled samples. Case studies conducted on a benchmark power system (China Electric Power Research Institute (CEPRI) 36-bus system) and a practical large-area power system (Northeast China Power System) reveal that the proposed approach outperforms conventional methods in terms of accuracy, label efficiency, scalability, and adaptability to operational variability.

Study on the reliability of nano-silver-coated tin solder joints for flip chips

Abstract The nano-silver-coated tin (Sn@Ag) paste was modeled using the method of the Anand unified viscoplastic constitutive model and elastic model. After thermal cyclic loading, the plastic strain of the solder joints increased cumulatively, while the maximum equivalent stress remained basically stable. The simulation results show that the maximum displacement occurs at the solder joint at the farthest end from the center of the chip, which is a dangerous solder joint. Using the finite element method and EPRI (the American Electric Power Research Institute) estimation method, the fatigue life of the nano-silver-coated tin solder joint is predicted to be 616 weeks, which is significantly higher than that of the nano-silver solder joint. It is indicated that adding a certain amount of nano-tin to the nano-silver paste to form a core–shell structure can improve the shear strength of the solder joint and reduce the plastic strain, thereby significantly improving the reliability of the solder joint. It is proved by experiments that the nano-silver paste is feasible for flip–chip interconnection. The research on this topic provides experimental reference and theoretical basis for the application of a new generation of interconnection materials in power devices and promotes the development and application of microelectronic packaging technology.

Measuring and Modeling the Skin Effect for Harmonic Power Flow Studies

This research aims to quantify the skin effect and estimate expressions that well represent the phenomenon for harmonic power flow studies. The primary focus is to validate the behavior of the skin effect at harmonic frequencies ranging from 60 Hz to 960 Hz, while considering various amplitudes of electric current. The investigation not only examines the measurement of the skin effect, but also considers the temperature of the tested conductors, aiming to analyze the increase in resistance resulting from temperature rise and resistivity changes. The measurement outcomes demonstrate notable increments in electrical resistance, with resistivity increases of up to 1.9% observed throughout the measurement process. Finally, based on the results obtained through laboratory measurements, mathematical expressions were estimated as a function of frequency. In order to evaluate the simulation time reduction by the proposed expressions, OpenDSS (version: 9.4.1.2; Electric Power Research Institute, Knoxville, TN, USA) software was used, which aims at quantifying the impact of the skin effect on the technical losses. The results from these simulations demonstrate that the proposed expressions to account for the skin effect in conductors reduce the simulation time by around 17% for harmonic power flow.

Occurrence of Large Geomagnetically Induced Currents Within the EPRI SUNBURST Monitoring Network

AbstractSpace weather, a natural hazard, can adversely impact human technological assets. High‐voltage electric power transmission grids constitute one of the most critical technological systems vulnerable to space weather driven geomagnetically induced currents (GICs). One of the major challenges pertaining to the study of GICs over the continental United States has been the availability of GIC measurements, which are critical for validation of geoelectric field and power flow models, for example. In this study, we analyze GIC measurements collected at 17 Electrical Power Research Institute (EPRI) SUNBURST transformer locations across the United States for which a GIC value of 10 A or greater was recorded. This data set includes 52 individual geomagnetic storms with Kp index 6 and above during the period from 2010 to 2021. The analysis confirms that there is a good correlation between the number of geomagnetic storms per year and the number of recorded GIC events. Our results also show that about 76% of the top 17 GIC events are associated with the storm main phase, while only 24% are attributed to storm sudden commencements. In addition, it is shown, for the first time, that mid‐latitude positive bays can cause large GICs over the continental United States. Finally, this study shows that the largest measured GIC event in the data set was associated with a localized intense dB/dt structure, which could be attributed to substorm activity.

Research on the Application of Information Management System in the Laboratory of Power Generation Enterprises

Information management systems have achieved many application results in the management of metrological calibration and chemical testing laboratories facing society, but there are few research and application cases that combine the two information systems. The power generation enterprise is equipped with both a metrological calibration laboratory and a chemical testing laboratory. Huadian Laizhou Power Generation Co., Ltd. and Huadian Electric Power Research Institute Co., Ltd. have jointly developed an information system that can manage both laboratory businesses simultaneously. Starting from practical cases, this article discusses the development feasibility of this information system, its differences from conventional laboratory information systems, and the innovation points implemented in the project from the perspectives of information technology and software function settings.

Irradiation of ultrasonic sensors and adhesive couplants for application in light water reactor primary loop piping and components

The Electric Power Research Institute (EPRI) Nuclear Sector and US Department of Energy Light Water Reactor Sustainability Program are committed to engaging in research and development endeavors to address materials aging issues specific to long term operation of light water power reactors. To this effect, EPRI launched an industry initiative to develop nondestructive evaluation systems for online monitoring of existing cracks in light water reactor primary coolant loop piping and components. One of the goals of this initiative is to develop a sensor system (or systems) that can determine nondestructively if cracks are growing or arrested and, in the case of the former, to characterize their growth rates. A missing component of this initiative is an experimental assessment of how sensors and adhesive couplants will perform in service when exposed to chronic energetic neutron radiation, particularly at the primary coolant loop hot and cold leg dissimilar metal welds, which join the primary loop piping to the reactor pressure vessel and reside in the vicinity of the reactor core. The objective of this experimental study was to determine how ultrasonic transducers and adhesive couplants perform when exposed to irradiation in a test reactor to simulate and accelerate in-service exposure. To achieve this objective, the signal stability of piezoelectric transducers and performance of adhesive couplants as a function of accumulated fast neutron fluence were characterized by collecting ultrasonic data in-situ during irradiation. Of particular interest were the ultrasonic signal quality and time decay of the amplitude of acoustic reflections as a function of fast neutron fluence. The results of the study showed that, of the 8 transducer/substrate sample assemblies tested, only 3 generated usable ultrasonic signals through the conclusion of the irradiation campaign. It was found that high temperature epoxy tends to ultrasonically couple the sensors to the substrates better than three types of refractory ceramic cements studied, as is supported by post irradiation examination. The results obtained through this experimental study will be utilized in the achievement of the overall goal of development of a sensor system to perform online monitoring of primary loop components.This manuscript has been authored in part by UT-Battelle, LLC, under contract DE AC05-00OR22725 with the US Department of Energy (DOE). The publisher acknowledges the US government license to provide public access under the DOE Public Access Plan (https://energy.gov/downloads/doe-public-access-plan [energy.gov]).

Stories From China

On February 19, 2023, the world's first set of 1,000-kV switch-type controllable metal oxide arresters (SCMOA) was officially put into operation at the 1,000-kV Beijing West (Baoding) substation and 1,000-kV Shijiazhuang (Xingtai) substation. The controllable arrester was co-developed by China Electric Power Research Institute, Pinggao Corporation Ltd., and NARI-Relays Electric Corporation Ltd. This is the first time an SCMOA has been used practically at a substation in China. The components are installed on two sides of the line to replace the closing resistor of the circuit breaker. By switching the controlled part of arrester, the overvoltage can be effectively suppressed. It can enhance the safety and reliability of operation. As an effective method to remove the closing resistor and limit overvoltage, the controllable arrester technique of SCMOA has been in the stage of engineering development.

Intelligent and rapid event-based load shedding pre-determination for large-scale power systems: Knowledge-enhanced parallel branching dueling Q-network approach

With the increasing penetration of renewable energy, power system instability factors are rising. Transient voltage instability is a common power system problem that can cause blackouts and severe economic losses. An important measure to ensure transient voltage stability during emergencies is event-based load shedding (ELS). However, formulating ELS measures by experts gradually becomes inadaptable and time-consuming currently. With the increased complexity and uncertainty of modern new power systems, there is an urgent need for more intelligent and rapid ELS. This paper proposes a knowledge-enhanced parallel branching dueling Q-network (BDQ) framework for intelligent and rapid ELS against transient voltage instability. Firstly, an event-based Markov decision process (MDP) that differs from the conventional response-based MDP is established, which can effectively guide the training process. Secondly, to condense the huge conventional exponential decision space, a multi-branch BDQ structure is designed, which has higher training effectiveness and decision capability compared to branchless agents. Then, the domain proprietary knowledge that low-voltage buses are prioritized for ELS is incorporated into the BDQ agent. In comparison with a purely data-driven BDQ approach, incorporating knowledge can significantly enhance both training effectiveness and decision capability. Next, to further improve the applicability in large-scale real power systems, the parallel BDQ is proposed. Finally, the advantages of the proposed approach are demonstrated in the China Electric Power Research Institute 36-bus system and the Western Electricity Coordinating Council 179-bus system.

Utilization of EPRI ChemWorks tools for PWR shutdown chemistry evolution modeling

Shutdown chemistry evolution is performed in nuclear power plants at each refueling outage (RFO) to establish safe conditions to open system and minimize inventory of corrosion products in the reactor coolant system (RCS). After hydrogen peroxide is added to RCS during shutdown chemistry evolution, corrosion products are released and are removed by filters and ion exchange resins in the chemical volume control system (CVCS). Shutdown chemistry evolution including RCS clean-up time to remove released corrosion products impacts the critical path schedule during RFOs. The estimation of clean-up time prior to RFO can provide more reliable actions for RCS clean-up operations and transients to operators during shutdown chemistry. Electric Power Research Institute (EPRI) shutdown calculator (SDC) enables to provide clean-up time by Co-58 peak activity through operational data from nuclear power plants (NPPs).In this study, we have investigated the results of EPRI SDC by shutdown chemistry data of Co-58 activity using NPP data from previous cycles and modeled the estimated clean-up time by EPRI SDC using average Co-58 activity of the NPP. We selected two RFO data from the NPP to evaluate EPRI SDC results using the purification time to reach to 1.3 μCi/cc of Co-58 after hydrogen peroxide addition. Comparing two RFO data, the similar purification time between actual and computed data by EPRI SDC, 0.92 and 1.74 h respectively, was observed with the deviation of 3.7–7.2%. As the modeling the estimated clean-up time, we calculated average Co-58 peak concentration for normal cycles after cycle 10 and applied two-sigma (2σ, 95.4%) for predicted Co-58 peak concentration as upper and lower values compared to the average data. For the verification of modeling, shutdown chemistry data for RFO 17 was used. Predicted RCS clean-up time with lower and upper values was between 21.05 and 27.58 h, and clean-up time for RFO 17 was 24.75 h, within the predicted time band. Therefore, our calculated modeling band was validated. This approach can be identified that the advantage of the modeling for clean-up time with SDC is that the primary prediction of shutdown chemistry plans can be performed more reliably during shutdown chemistry. This research can contribute to improving the efficiency and safety of shutdown chemistry evolution in nuclear power plants.

Comparison of nano-silver solder joints and SAC305 based on ANSYS simulation and life prediction

With the rapid development of microelectronic interconnection technology, the reliability requirements of electronic products are becoming higher and higher. Among them, temperature has the greatest impact on electronic devices. Due to the different coefficients of thermal expansion (CTE) between the many materials of a chip, the inside of a solder joint is subjected to cyclic temperature action. Under the effect of cyclic temperature, the solder joints are subject to internal fracture resulting in the failure of the solder joint. Therefore, it is necessary to find a more reliable material for the solder joint. In this paper, the advantages and disadvantages of pure silver material and low silver material are compared by finite element simulation analysis of nano-silver pure silver material and SAC305 low silver material, and the fatigue life prediction of nano-silveris predicted by a life prediction model. Then, using the Electric Power Research Institute estimation method to estimate the fatigue life of solder joints, the results are compared with those calculated by the finite element method.

Seismic Evaluation Approaches for Spent Fuel Pool Structures in Nuclear Power Plants

The United States Nuclear Regulatory Commission issued requests for licensees to re-evaluate the seismic hazards at their sites after the accident at the Fukushima Daiichi Nuclear Power Plant in Japan on March 11 in 2011 and to identify and address any site-specific vulnerabilities associated with seismic hazards. The primary guidance for performing those evaluations is provided in the Electric Power Research Institute EPRI-1025287 report, which also provides guidance for evaluating spent fuel pool (SFP) integrity. In addition, the EPRI-3002009564 report also provides evaluation approaches regarding the effects of seismic ground motions on SFPs that supplement the guidance provided in EPRI-1025287. SFP integrity has become increasingly important for active and decommissioned nuclear power plants. According to EPRI-1025287, the SFP integrity evaluation emphasizes failure modes of the SFP that could result in “rapid drain-down.” The definition of “rapid drain-down” is a failure that could lead to the uncovering of irradiated fuel stored in the SFP within 72[Formula: see text]h of an earthquake. Possible failures can be classified into two categories: failures relevant to the SFP structure and failures relevant to non-structural elements. This paper aims to study the approaches of implementing seismic evaluation of an SFP structure. EPRI-3002009564 provides separate seismic evaluation approaches for plants with a ground motion response spectrum (GMRS) peak [Formula: see text][Formula: see text]g and for plants with a GMRS peak [Formula: see text][Formula: see text]g. Structural dynamic analysis is also a common approach for implementing seismic evaluation if a detailed finite element model is available. In this paper, a sample SFP structure was evaluated using the two approaches, structural dynamic analysis and structural analysis criteria. The results indicate that shear failure controlled the failure mode of the SFP structure for both approaches. This shows that the two approaches drew the same conclusion regarding the failure mode. Furthermore, a smaller seismic margin was obtained using the structural analysis criteria, which means this evaluative approach is more conservative.

Corrigendum: Static equivalent of distribution network with distributed PV considering correlation between fluctuation of PV and load

Incorrect AffiliationIn the published article, there was an error in affiliation(s) [1,2]. Instead of “[Electric Power Research Institute, State Grid Shandong Electric Power Company, Jinan, China; Shandong Electric Power Company, State Grid Corporation of China, Jinan, China]”, it should be “[Power Grid Technology Center, State Grid Shandong Electric Power Research Institute, Jinan, China; Shandong Electric Power Dispatching and Control Center, State Grid Shandong Electric Power Company, Jinan, China]”. The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way. The original article has been updated.Incorrect Author NamePlease also check that the initials used in the Author Contributions section or elsewhere in the article are correct. In the published article, an author name was incorrectly written as [Kang Zhao2]. The correct spelling is [Kang Zhao1]. The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way. The original article has been updated.

Ground-motion model for the standardized version of cumulative absolute velocity

After publishing its original definition of cumulative absolute velocity ( CAV), the Electric Power Research Institute (EPRI) proposed a standardized version of CAV that it recommended is a better indicator of damage to structures of good design and construction than CAV. We refer to this intensity measure (IM) as CAVSTD. EPRI proposed 0.16 g-s (1.57 m/s) as the threshold value of CAVSTD that corresponds to the onset of damage to structures of good design and construction. Although this damage threshold was conservatively applied to nuclear power plants, its development using recordings from sites subjected to MMI VII shaking suggests that it is appropriate for civil structures. In 2011, we developed a ground-motion model (GMM) for the version of CAVSTD that was adopted by the US Nuclear Regulatory Commission for determining when a nuclear power plant must be shut down for inspection after an earthquake, which we called CAVDP. In this study, we develop a GMM for CAVSTD conditioned on values of CAV and peak ground acceleration ( PGA) using an extensive database of recordings compiled for the NGA-West2 project. We demonstrate how the conditional GMM developed in this study can be used together with predicted values of CAV and PGA to provide unconditional estimates of CAVSTD and its standard deviations when values of these IMs are unknown.

Investigations of In-Plane Fluidelastic Instability in a Multispan U-Bend Tube Array—Part II: Tests in Two-Phase Flow

Abstract Tests to study fluidelastic instability (FEI) in an array of U-bend tubes were recently completed in the multispan U-Bend test rig at Canadian Nuclear Laboratories. These tests were sponsored by the Electric Power Research Institute and were designed to study in-plane fluid elastic instability of steam generator tubes in two-phase cross flow. This instability mechanism was first observed in previous experiments by Atomic Energy of Canada Limited. This mechanism was not thought to be a serious practical concern until 2012 when it caused severe damage to tubes in a new replacement steam-generator in a nuclear power plant in the United States. In this study, tests were conducted both with flows of air and two-phase liquid/vapor Refrigerant 134a. The tube bundle consisted of 22 flexible U-bend tubes supported by a configurable flat-bar arrangement. Testing focused on the effects of support geometry and tube-to-support interaction. Data were recorded from 33 dynamic signals from accelerometers, displacement probes, force transducers, and void-fraction probes. Part I of this two-part series presented results of air tests. Part II presents results of tests using two-phase Freon refrigerant (R-134a) as the working fluid.

Investigations of In-Plane Fluidelastic Instability in a Multispan U-Bend Tube Array—Part I: Tests in Air Flow

Abstract The tubes in the U-bend region of a recirculating type of nuclear steam generator are subjected to cross-flow of a two-phase mixture of steam and water. There is a concern that these tubes may experience flow-induced vibration, including the damaging effects of fluidelastic instability. This two-part series of papers presents the results of flow-induced vibration experiments performed by Canadian Nuclear Laboratories for the Electric Power Research Institute (EPRI) using the Multi-Span U-Bend test rig. The tube bundle is made of 22 U-bend tubes of 12.7 mm (0.5 in.) diameter, arranged in a rotated triangular configuration with a pitch-to-diameter ratio of 1.5. The test rig was equipped with variable clearance flat bar supports at two different locations to investigate a variety of tube and flat-bar support configurations. The primary purpose of the overall project was to study the occurrence of in-plane (or streamwise) fluidelastic instability in a U-tube bundle with flat-bar tube supports with clearances or preloads. Initially, the test rig was configured for tests in air-flow using an industrial air blower. Then tests with two-phase refrigerant (R-134a) were performed. Part I of this two-part series describes the test rig, experimental setup and some of the challenges encountered, and the results of experiments with air flows. Part II will present results of tests using refrigerant two-phase flows.

Role of welding residual stress in stainless steel piping with application of the leak-before-break technology

The predicted leakage rate of piping circumferential through-wall cracks (CTWC) under various loading levels is a critical factor for the application of leak-before-break (LBB) technology. In current engineering approaches, the effect of welding residual stress has not been carefully taken into account. In this paper, both numerical analyses and comparative verification are adopted to examine the influence of typical welding residual stress field on the crack opening displacement for austenitic stainless steel piping with representative geometric dimensions and in situ measured material performance curves. An in-depth investigation is carried out to reveal the effect of the residual stress on morphological parameters of the CTWC flow channel. In the case where the residual internal stress of welding has the greatest effect, the Henry-Fauske model is employed to analyze the flow medium passing through the CTWC and the corresponding leak rate for a typical nuclear power plant. The results indicate that the welding residual stress leads to a substantial change in the crack opening displacement and crack morphology parameters. Both the current GE/EPRI method and the NUREG/CR-6837 modification recommended by the American Electric Power Research Institute underestimate the effect of this phenomenon, resulting in a higher prediction of the medium leakage rate. A similar situation is most likely to occur for the cases of short cracks in thin-walled piping and long cracks in thick-walled piping. Additionally, the obtained results reveal that the welding residual stress causes the whole crack surface to open negatively, and the axial line of the long crack on the thick-walled piping is close to a conic curve under specific conditions.

Corrigendum: Small-signal stability analysis of the power system based on active support of renewable energy VSCs

In the published article, there was an error in the Author list and Address section, and authors Shunjiang Wang,Tianfeng Chu and Miao Xu were inserted in the wrong order, so the authors' addresses were inserted in the wrong order. The corrected Author list and Address section appear below.Tianfeng Chu1,2, Miao Xu3, Yu Xie4, Shunjiang Wang3, Dianyang Li3 and Gang Liu3.1 College of Information Science and Engineering, Northeastern University2 Electric Power Research Institute of State Grid Liaoning Electric Power3 the State Grid Liaoning Electric Power 4 Northeast Electric Power University.The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way. The original article has been updated.